Biocomposite materials and methods for making the same

ABSTRACT

A particle (and a composition that includes a plurality of the particles) that includes at least one polypeptide molecule and at least one polymer covalently bound to the polypeptide molecule so as to form a polymer shell substantially encompassing the polypeptide molecule, wherein the particle does not define a dimension greater than about 1 μm. One example for making the particle includes modifying the polypeptide molecule to provide α, β-ethylenically unsaturated terminal functional groups, mixing the modified polypeptide molecule with a silicon-containing polymerizable compound, and subjecting the resulting mixture to conditions sufficient for polymerizing the polymerizable compound to form the particle.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with United States Government support underContract DE-AC0 6-76RL01830 awarded by the U.S. Department of Energy.The United States Government has certain rights in the invention.

BACKGROUND

Polypeptides or proteins, such as enzymes, are useful nanoscalebio-macromolecules, but the short lifetime of these nanobiologicalsystems presently limits their usefulness. Enzyme immobilization is oneof the most important methodologies that can provide enzymestabilization. However, previously developed stable enzyme systemsgenerally provide poor enzyme activity. Conversely, previously developedactive enzyme systems generally display poor enzyme stability. Despitesignificant efforts, the development of enzyme systems that are bothactive and stable continues to be a great challenge.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain examples are described below with reference to the followingfigures:

FIG. 1 is a schematic diagram of one example of synthesizingbiocomposite nanoparticles.

FIG. 2 shows the chemical synthesis of one example of biocompositenanoparticles.

FIGS. 3, 4 and 5 are transmission electron microscopy (“TEM”) images ofexamples of biocomposite nanoparticles. The scale bars in the bottomleft corners of the images represent 50 nm (FIG. 3) and 100 nm (FIGS. 4and 5), respectively.

FIG. 6 is a graph depicting the stability of α-chymotrypsin biocompositenanoparticles (∘, 10 μg/ml; Δ, 1 μg/ml; □, 0.1 μg/ml) and free CT (•, 10μg/ml; ×, 1 μg/ml; ▪, 0.1 μg/ml). Residual activity was determined bythe hydrolysis of TP in aqueous buffer (10 mM sodium phosphate, pH 7.8)after incubation at 30° C. All the incubation was done in plastic tubessince the α-chymotrypsin biocomposite nanoparticles covalently bound tothe inner surface of glass vials.

DETAILED DESCRIPTION OF SEVERAL EXAMPLES

For ease of understanding, the following terms used herein are describedbelow in more detail:

“Nanoparticle” denotes a discrete particle that does not have anydimension greater than about 1 μm.

“Polypeptide” refers to a polymer in which the monomers are amino acidresidues that are joined together through peptide bonds, and encompassesany amino acid sequence, including modified sequences such asglycoproteins. “Proteins” encompasses proteins, fragments thereof, andconjugated proteins. The term “polypeptide” or “protein” is specificallyintended to cover naturally occurring proteins, as well as those thatare recombinantly or synthetically produced. Functional fragments of apolypeptide or protein refers to all fragments of a polypeptide orprotein that retain an activity, or a measurable portion of an activity,of the polypeptide or protein from which the fragment is derived.Fragments, for example, can vary in size from a polypeptide fragment assmall as an epitope capable of binding an antibody molecule to a largepolypeptide capable of participating in the characteristic induction orprogramming of phenotypic changes within a cell.

“Silyl” refers to a functional group having a structure represented by—SiH₃.

“Substituted silyl” refers to a functional group having a structurewherein at least one of the hydrogen molecules of a silyl group havebeen replaced with another functional group such as an alkoxy or hydroxygroup.

The above term descriptions are provided solely to aid the reader, andshould not be construed to have a scope less than that understood by aperson of ordinary skill in the art or as limiting the scope of theappended claims.

Disclosed herein are unique biocomposite materials that generallyinclude at least one polypeptide or protein molecule partially orsubstantially encapsulated within an organic/inorganic shell. The shelltypically is sufficiently porous so that the shell does notdeleteriously interfere with the bioactivity of the protein. Forexample, the shell may be sufficiently porous to allow the encapsulatedprotein to digest substrates having molecular weights up to about 70kilodaltons. The ability to permit digestion of relatively largesubstrates can substantially increase the range of substrates that canbe used with the biocomposite materials. Another characteristic of thebiocomposite materials is that they generally exhibit a minimal, if any,mass-transfer limitation between the protein molecule and a substrate.For example, the biocomposite materials may have an observedeffectiveness factor (OEF or η) of at least about 0.7, and moreparticularly about 0.9. The OEF, defined by the ratio of reaction rateswith and without the shell, may be calculated by dividing the apparentbinding constant (K_(m) ^(app)) of the free protein (i.e., a proteinmolecule that is not bound to the polymer shell) by the K_(m) ^(app) ofthe biocomposite. The effective porosity of the shell may be adjusted,for example, by controlling the extent of chain-extension polymerizationand polymer crosslinking as described in more detail below.

On the other hand, the shell may be sufficiently bound to the protein toform an effective thermodynamic barrier for increasing the stability ofthe polypeptide's or protein's bioactivity. For example, if theencapsulated protein is an enzyme, substrates for the enzyme may diffusethrough the shell but the shell contributes to increasing the activationenergy required for transition of the protein from the native form tothe denatured form. The inorganic domain of the shell further providesadditional hardness and structural integrity to the biocomposite, andthus enables the biocomposite to better withstand structural stress andfrictional forces during use of the biocomposite. Consequently, thebiocomposite dramatically stabilizes the enzyme activity.

The biocomposite materials typically are in the form of solidnanoparticles. The nanoparticle may assume a variety of geometricalshapes such as generally spherical, oval, tubular, or asymmetrical. Theshape of nanoparticles that contain only a single protein or polypeptidemolecule in the nanoparticle core generally will be similar to the shapeof the native or free protein or polypeptide molecule. The shelltypically has an average thickness of only about 0.2 to about 200 nm,more particularly about 1 to about 50 nm. In the case of nanoparticlesthat contain only a single protein or polypeptide molecule, the shellthickness may be more particularly about 0.2 to about 10 nm, especiallyabout 1 to about 5 nm. The shell forms a distinct or discrete layer atthe surface of the polypeptide or protein molecule, which may bevisually discernible under appropriate magnification for nanoparticlesthat contain only a single protein or polypeptide molecule (see FIGS. 3and 4 described below). Consequently, the nanoparticles generally do nothave any dimensions that are greater than about 1 μm. The nanoparticlesoften do not have a dimension greater than about 200 nm, moreparticularly about 100 nm, and even more particularly not greater thanabout 50 nm. There is no critical limitation on the minimum size of thenanoparticle, but the nanoparticle typically defines a dimension of atleast about 2 nm.

The biocomposite material can be formed from at least one polypeptide orprotein or a mixture of different types of polypeptides or proteins. Theprotein may be, for example, an enzyme, a hormone, a toxin, an antibody,an antigen, a lectin, a structural protein, a signal protein, atransport protein, a receptor, a blood factor, or a mixture thereof.According to particular examples, the protein is an enzyme such asproteases (e.g., chymotrypsin, trypsin, subtilisin, and papain),lipases, peroxidases (e.g., horseradish peroxidase, soybean peroxidase,chloro peroxidase, and manganese peroxidase), tyrosinase, laccase,cellulase, xylanase, lactase, sucrase, organophosphohydrolase,cholinesterase, glucose oxidase, alcohol dehydrogenase, glucosedehydrogenase, hydrogenase, and glucose isomerase. In a specificvariant, the nanoparticle biocomposite includes a single proteinmolecule encompassed by the shell. However, the core may be a proteinconstruct that includes more than one protein molecule. For example,several polypeptide or protein molecules may be crosslinked together bycontacting the polypeptide or protein molecules with glutaraldehyde,toluene diisocyanate, or diphenylmethane diisocyanate. The polypeptideor protein may be a fusion protein. As used herein, “protein moleculecore” encompasses such plural-molecule constructs.

Specific examples of nanoparticle cores that include more than onepolypeptide or protein molecules are cores that could perform sequentialtransformations on a substrate by two or more enzymatic reactions. Thus,the nanoparticle could be a bioreactor executing more than onetransformation to convert a molecule into a desired product. Forexample, the nanoparticle bioreactor could include appropriatepolypeptide or protein molecules to replicate a metabolic pathway withinliving tissue. The close proximity of the core proteins that can beobtained with the nanoparticles will promote the sequential reactions.

One illustrative plural-molecule core is a system that includes aglucose oxidase molecule and a peroxidase molecule in the core. Theglucose oxidase can convert glucose to glucuronic acid and hydrogenperoxide. The hydrogen peroxide can be used for the peroxidase reactionwith a reporter fluorescence molecule (for glucose biosensing) or aphenol (for bioremediation of phenol). Another illustrative example is asystem that includes glucose dehydrogenase and hydrogenase in the core.The glucose dehydrogenase can convert glucose into glucuronic acid, andreduce nicotinamide adenine dinucleotide phosphate (NADP) to reducednicotinamide adenine dinucleotide phosphate (NADPH). The NADPH can beused for the hydrogenase reaction to produce hydrogen. A furtherillustrative example is a system that includes invertase, glucosedehydrogenase, and hydrogenase in the core. The invertase cleavessucrose to glucose and fructose, and glucose can be used for theproduction of hydrogen via catalysis with glucose dehydronase andhydrogenase as described above. Glucose isomerase may be added forconverting fructose to glucose. Certain enzymes can also be included inthe particle core construct for producing glucose from target moleculesin agricultural biomass. For instance, cellulase, xylanase, and lactase(β-glucosidase) can be employed for hydrolyzing cellulose, xylan, andlactose, respectively, into their constituent sugars.

The nanoparticle biocomposites can be provided in a variety of usefulforms or media. For example, a multitude of individual nanoparticlescould be dried resulting in a powder composition. The nanoparticles maybe dispersed, suspended or dissolved in a liquid media. Thenanoparticles may be dissolved in water such as an aqueous buffer or anorganic solvent (provided the polymer shell has been functionalized withappropriate hydrophobic groups). The versatility of the solubility ofthe nanoparticles is advantageous since many enzymatic syntheticreactions can occur in aqueous or organic solvents.

The composite shell usually is chemically bound to the polypeptide orprotein. The chemical bond may be any type of bond, but covalent bondingis especially useful. The chemical bond is primarily formed withfunctional groups or moieties that are present on or near the surface ofthe protein as described below in more detail.

A feature of the polymer shell is that there is substantially nocrosslinking between each individual polymer-encapsulated proteinmolecule core. Each nanoparticle is a discrete particle having a proteinconstruct core substantially encapsulated only by an individual polymershell. In other words, the crosslinking occurs only between polymerschains covalently attached to the same protein molecule core. There issubstantially no inter-protein crosslinking between a first polymerchain covalently attached to a first protein molecule and a secondpolymer chain covalently attached to a second protein molecule that isspaced apart from the first protein molecule. According to the synthesisdisclosed herein, the crosslinking may be limited to prevent theformation of a polymer network or matrix that encapsulates a pluralityof spaced-apart protein molecules. Examples of such inter-proteincrosslinked polymer networks are shown, for instance, in U.S. Pat. No.6,291,582 (FIG. 1) and Norvick et al., “Investigating the Effects ofPolymer Chemistry on Activity of Biocatalytic Plastic Materials”,Biotech. and Bioeng., 68, 665-671 (FIG. 1).

The shell material may include at least one inorganic moiety. Oneexample is a silicon-containing moiety or functional group such as asilane or a siloxane functional group. In an illustrative example theshell may be a polysiloxane such as a polyorganosiloxane. Thepolysiloxane is covalently bound to the protein via linking groups. Oneexample of linking groups is residues produced fromethylenically-unsaturated carbon functional groups, particularly vinylgroups, that have undergone addition polymerization.

Synthesis

According to one illustrative synthesis approach, the process begins atthe surface of the polypeptide or protein molecule, with covalentreactions to anchor, grow, and crosslink an individual polymer compositeshell around each protein molecule. The process may involve two-phasereaction and extraction systems, as well as selective filtering orseparation to isolate the biocomposite nanoparticles. Examples ofparticular process steps are described below in more detail.

A polypeptide or protein molecule typically is initially contacted witha modifier compound so that the free amino, carboxyl, and/or sulfidegroups of the protein are modified to include (a) a reactive group thatis polymerizable with at least one second compound, or (b) a reactivegroup that by itself can undergo subsequent polymerization. The option(a) approach will be described first.

The second compound in the option (a) approach may be referred tothroughout this application as the “shell-forming compound.” Thepolymerizable reactive groups, along with reactive groups of the secondcompound, provide the covalent bonding of the organic/inorganic polymershell to the individual protein molecule. In addition, the modifyingreactive groups can assist in solubilization of the protein in anorganic solvent.

The modifier compound includes a functional group that is reactive withfree amino groups, carboxyl, and/or thiol present in the proteinmolecule to provide the desired functionalization of the proteinmolecule. Typical amino-reactive groups include carboxy groups (—COOH);carboxylate ionic groups (—COOX, wherein X is selected from a halogensuch as Cl or Br); carbonyl halide groups (—COX, wherein X is a halogenselected from Cl, Br, F or I); succinyl groups (—OCCH₂CH₂CO—); epoxygroups; and isocyanato groups. Typical carboxyl-reactive groups includeamino groups such as a diimide linker (e.g.,1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride).

The group of the modifier compound that is reactive with theshell-forming compound may be an α, β-ethylenically unsaturated terminalfunctional group such as, for example, a vinyl group or an allyl group.According to a specific example, a vinyl group functionality is graftedonto the surface of enzymes by covalently modifying substantially mostof the amino groups on the enzyme surface. Suitable modifier compoundsinclude vinyl compounds such as (meth)acrylic acid, (meth)acrylate,substituted (meth)acrylate, and acryloyl chloride. Such vinyl compoundsshould also include amino, carboxyl, and/or sulfide-reactive groups forforming a covalent bond to the polypeptide or protein molecule asdescribed above.

Further examples of possible modifier compounds include polyethyleneglycol compounds. Polyethylene glycols can include terminal functionalgroups such as amino, carboxyl, hydroxy, thiol, and acryl groups thatcan be reacted with the polypeptide or protein molecule in an aqueousbuffer. Thus, the polyethylene glycol chain can be covalently bonded tothe surface of the polypeptide or protein molecule. Acrylatedpolyethylene glycol and similar compounds described, for example, inU.S. Pat. No. 5,482,996 and Yang et al., “Activity and Stability ofEnzymes Incorporated into Acrylic Polymers”, J Am. Chem Soc. 1995, 117,4843-4850. The polyethylene glycol can also include a pendant functionalgroup that is reactive with a shell-forming compound. Such functionalgroups include amino, carboxyl, and/or hydroxyl groups. Crosslinking ofthese functional groups with a shell-forming compound is described inmore detail below.

The modifier compound may be mixed with the polypeptide or protein underany conditions sufficient for achieving the desired terminal groupmodification. For example, the protein may be dissolved in an aqueoussolution such as a buffered solution. The modifier compound then ismixed into the protein-containing buffer and allowed to react with theprotein molecules. In the case of nanoparticle core constructs thatinclude more than one protein molecule, the individual protein moleculesmay be each initially surface-modified and then linked together to formthe core construct. The amount of modifier typically is sufficient tomodify a substantial amount, if not all, of the free amino, carboxyl,and/or sulfide groups. The temperature of the reaction mixture iscontrolled so as to avoid damaging the bioactivity of the proteinmolecules. One example of a possible temperature range is from about 0°C. to about 4° C. The buffer is used to maintain the pH of the aqueoussolution at the desired level. For example, if an anionic or cationicsurfactant is used for solubilizing the protein in an organic solvent,then the pH of the aqueous solution is adjusted accordingly to providethe protein with an appropriate negative or positive net surface charge.Alternatively, if a certain protein has an optimal pH range forbioactivity and stability, then a suitable anionic or cationicsurfactant can be selected depending upon the net surface charge of theprotein. For example, protein molecules will be positively charged ifthe pH value of the buffer solution is lower than the protein's pI, andwill be negatively charged if the pH value is higher than the protein'spI. Specific illustrations of this approach include α-chymotrypsin whichhas a pI of 8.8 and an optimal pH of 7.8 for bioactivity. Thus, the netsurface charge of α-chymotrypsin at a pH of 7.8 is positive, meaningthat an anionic surfactant should be employed. Similarly, trypsin has apI of 10.2 and optimal bioactivity pH of 8, and thus an anionicsurfactant also would be utilized. Tyrosinase, on the other hand, has apI of 4.7 and an optimal bioactivity pH of 6.5. Accordingly, a cationicsurfactant would be used with tyrosinase.

The α, β-ethylenically unsaturated-modified proteins typically areinsoluble or display limited solubility in organic solvents. On theother hand, many polymerizable compounds useful for forming thecovalently-bound shell are soluble in organic solvents, but not inwater. Thus, an optional step in the synthesis disclosed herein involvessolubilizing the modified protein in an organic solvent. There are atleast two solubilizing techniques that may be suitable. One technique isdescribed in more detail below and involves the use of surfactants. Theother technique involves modifying the protein surface with hydrophobicfunctionality such as acrylated polyethylene glycol (see U.S. Pat. No.5,482,996 and Yang et al., “Activity and Stability of EnzymesIncorporated into Acrylic Polymers”, J Am. Chem Soc. 1995, 117,4843-4850). Alternatively, certain useful polymerizable compounds may bewater-soluble as described in more detail below. In this alternativescenario, solubilizing of the modified protein in an organic solvent maybe avoided, and synthesis may proceed directly to polymerization withthe shell-forming compound in an aqueous media.

If the optional protein solubilizing step is employed, one approachinvolves utilizing a surfactant. In particular, a two-phase system isprovided wherein a first phase includes an aqueous solution of themodified protein, and the second phase includes a surfactant dissolvedin an organic solvent. The two-phase system is mixed together and formsa protein-surfactant complex. A substantial portion, if not all, of theprotein-surfactant complex is extracted into the organic phase.

If an anionic or cationic surfactant is employed, the protein-surfactantcomplex may be formed by generating a modified protein that has a netsurface charge that is opposite the charge of the selected surfactant.Illustrative anionic surfactants include fatty alcohol sulfates,including sodium, potassium, ammonium or triethaniolamine salts ofsaturated or unsaturated C₁₀ to C₁₈ hydrocarbons such as sodium dodecylsulfate (SDS), sodium tetradecyl sulfate, sodium heptadecyl sulfate, andsodium lauryl sulfate (SLS); sodium 2-ethylhexyl sulfate; ethoxylatedfatty alcohol sulfates, including alkyl ether sulfates such as sodiumlauryl ether sulfate (SLES); sarconisate; alkyl glyceryl ethersulfonate; alpha sulpho fatty acids and esters; fatty acid esters ofisethionic acid; acyl (fatty) N-methyltaurides; dialkylsulfo succinateesters including C₈, C₁₀ and C₁₂ forms thereof such as bis(2-ethylhexyl)sodium sulfosuccinate (AOT); N-acylated amino acids, such as sodiumN-lauroyl sarconisate or gluconate; sodium coconut monoglyceridesulfonate; alkyl phosphates such as (2-ethylhexyl) phosphate; andtauroglycocholate. Illustrative cationic surfactants include compoundscontaining quaternary ammonium hydrophilic moieties in the moleculewhich are positively charged, such as quaternary ammonium salts or basesthat include alkyl groups containing 1-30 carbon atoms, or alkyl groupsderived from tallow, coconut oil, or soy; hydroxide; and or halogen.Dialkyl dimethyl ammonium salts and monoalkyl trimethyl ammonium saltsmay be used. Representative quaternary ammonium salts and hydroxidesinclude dodecyltrimethyl ammonium chloride/lauryltrimethyl ammoniumchloride (LTAC), cetyltrimethyl ammonium chloride (CTAC),didodecyldimethyl ammonium bromide, dihexadecyldimethyl ammoniumchloride, dihexadecyldimethyl ammonium bromide, dioctadecyldimethylammonium chloride, dieicosyldimethyl ammonium chloride,didocosyldimethyl ammonium chloride, dicoconutdimethyl ammoniumchloride, ditallowdimethyl ammonium chloride, ditallowdimethyl ammoniumbromide, cetyltrimethyl ammonium hydroxide, andtetradecyltrimethyl-ammonium bromide (TTAB). Nonionic surfactants suchas, for example, octylphenol ethylene oxide condensates (e.g., TRITONX-100), and silicone block copolymers (e.g., SILWET) could also be used.

An organic solution containing the desired surfactant is prepared,typically by simply mixing the surfactant with an organic solvent.Illustrative organic solvents include alkanes having at least fivecarbon atoms such as hexane, isooctane, and octane; aromatichydrocarbons such as benzene or toluene. The surfactant concentrationshould be below the critical micellar concentration that would result ina reverse micelle. On the other hand, the surfactant concentrationshould be sufficient to form the protein-surfactant complex resulting inthe solubilization of the protein in the solvent. A particularsurfactant concentration range depends on the size of the proteinmolecule and the hydrophobicity of the surfactant molecule. For example,1 mM AOT may be used for the solubilization of 1 mg/ml α-chymotrypsin.

The organic surfactant solution then is intimately mixed with theaqueous modified protein solution, typically at room temperature (i.e.,about 20-25° C.). The modified protein concentration in the resultingmixture may range, for example, from about 1 μg/ml to about 10 mg/ml.The pH of the resulting mixture may range from about 2 to about 12,depending upon the optimal pH for the bioactivity of the particularprotein. The volume ratio of the organic surfactant solution relative tothe aqueous modified protein solution can range from about 1:10 to about10:1. The resulting mixture then is phase-separated by centrifugation orsimilar techniques. Phase separation can also occur simply by allowingthe mixture to rest without performing any additional separationtechniques. The modified protein is extracted into the organic phaseresulting in the formation of the protein-surfactant complex. Theprotein-surfactant complex may be isolated by drying or otherwiseremoving the organic liquid and other components. Additives may beincluded in the organic/aqueous mixture to provide a higher proteinextraction ratio and improved phase separation. For example, inorganicsalts such as CaCl₂ and KCl may improve phase separation. Hydrophilicsmall molecules such as 1-propanol and 2-propanol may provide a higherextraction ratio.

With reference back to the general synthesis procedure, the modifiedpolypeptide or protein is contacted with at least one shell-formingcompound. A mixture of shell-forming compounds may be simultaneouslycontacted with the modified polypeptide or protein, or individualshell-forming compounds may be successively or stepwise contacted withthe modified polypeptide or protein. As described above, the modifiedpolypeptide or protein may or may not have undergone solubilizationtreatment prior to contact with the shell-forming compound. Theshell-forming compound may be a polymerizable compound that is capableof forming chemical bonds with the modified functional groups on thesurface of the polypeptide or protein. The polymerizable compound may bea monomer, an oligomer, a prepolymer, or a polymer that can be furtherpolymerized. A mixture of polymerizable compounds may be used to achievea variety of properties and characteristics for the polymer shell. Thechemical bonding and polymerization with the shell-forming compound canoccur in either an organic or aqueous system. For example, if theshell-forming compound is soluble or dispersible in water, then organicsolubilization of the modified polypeptide or protein is not necessary,and the polymerization can be performed in an aqueous system. On theother hand, if the shell-forming compound is only soluble or dispersiblein an organic solvent, then organic solubilization of the modifiedpolypeptide or protein may be desirable so that polymerization can beperformed in an organic system.

According to a representative example, the polymerizable compoundincludes at least one polymerizable carbon-unsaturated bond and at leastone substituted silyl group such as an alkoxysilyl or hydroxysilylmoiety. The polymerizable unsaturated bond may be an α, β-ethylenicallyunsaturated bond. Examples of such carbon-unsaturated silane compounds(interchangeably referred to herein as “silicate” compounds) may havethe representative formula (I):R_(a)SiX_((4-a))wherein each R represents an organic moiety that includes at least onecarbon-unsaturated bond and in which a carbon atom is bonded directly tothe silicon atom, and; a is an integer from 1 to 3; and each Xrepresents at least one moiety selected from a hydroxyl group, an alkoxygroup, a siloxy group, an alkyl group, a carboxyl group, or an aminogroup; and wherein each R moiety may be the same or different and each Xmoiety may be the same or different. According to certain examples ofthe silane compound, at least one of the X moieties is an alkoxy group.Vinyl silanes may be particularly suitable.

More specific examples of silane compounds are (meth)acryloxy-containingorganosilanes, more particularly a (meth)acryloxy-containingalkoxysilane having the following representative formula (II):CH₂═CH(R¹)—C(O)—O—(R²)—Si(R³)_(a)(OR⁴)_(3-a)wherein R¹ represents hydrogen or a methyl group; R² represents adivalent hydrocarbon moiety; each R³ represents hydrogen or an alkylgroup; each R⁴ represents an alkyl group; and a is an integer from 0 to2. R² may be an alkylene or substituted alkylene group that includes 1to 10 carbon atoms such as, for example, —CH₂—, —CH₂—CH₂—,—CH₂—CH₂—CH₂—, or —CH₂—CH(CH₃)—CH₂—. The alkyl group for R³ or R⁴ mayinclude 1 to 10 carbon atoms, more particularly 1 to 5 carbon atoms.(Meth)acryloxy-containing organosilanes tend to be more reactivecompared to vinyl silanes (e.g., vinyltrimethoxysilane) or allyl silanes(e.g., allyltrimethoxysilane) that do not contain (meth)acryloxyfunctional groups. Thus, the vinyl group polymerization can be initiatedby a relatively reduced amount of initiator, and reach desiredcompletion in a shorter time span.

Illustrative examples of carbon-unsaturated silanes includevinyltrimethoxysilane, vinyltriethoxysilane,vinyltris-(β-methoxyethoxy)silane,γ-methacryloxypropylmethyldimethoxysilane,γ-methacryloxypropyltrimethoxysilane,γ-methacryloxypropylmethyldiethoxysilane,γ-methacryloxypropyltriethoxysilane, γ-acryloxypropyltrimethoxysilane,γ-acryloxypropyltriethoxysilane, vinyltriisopropoxysilane,vinyldimethylmethoxysilane, allyltrimethoxysilane, allyltriethoxysilane,allylaminopropyltrimethoxysilane, allyldimethoxysilane,vinyltributoxysilane, vinyltriisopropoxysilane,vinylmethyldiethoxysilane, and vinylmethyldimethoxysilane.

Acrylic acid and (meth)acrylates are additional examples ofpolymerizable, shell-forming compounds that could be reacted with avinyl-functionalized polypeptide or protein molecule in aqueous buffer.Suitable water-soluble acrylates include acrylic acid, methyl acrylate,ethyl acrylate, and butyl acrylate.

In the case of a polyethylene glycol as the proteinsurface-functionalizing compound, the shell-forming compound may be anycompound that can crosslink amino, carboxyl, and/or hydroxyl pendantgroups. Such shell-forming compounds include dialdehydes such asglutaraldehyde; isocyanates such as toluene diisocyanate,diphenylmethane diisocyanate; carbodiimides such as1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (withlysine); polyethyleneimine; glycine; and lysine.

The polymerization of the modified polypeptide or protein with thepolymerizable or shell-forming compound may be accomplished by anypolymerization mechanism such as, for example, condensation or additionpolymerization. In the case of a carbon-unsaturated silane as theshell-forming compound the polymerization occurs in two steps. The firststep involves addition polymerization of the α, β-ethylenicallyunsaturated functional group of the modified polypeptide or protein withthe carbon-unsaturated functional group of the carbon-unsaturated silanecompound. The second step involves hydrolysis and condensation of thesilicon-containing functional groups derived from the carbon-unsaturatedsilane compound to produce a crosslinked polyorganosiloxane. The finalproduct is a nanoparticle that includes the polyorganosiloxane as ashell covalently bound to the polypeptide or protein molecule.

In an illustrative example, the addition polymerization involves vinylgroup polymerization to chain-extend linear polymers on the proteinsurface. The linear polymers on the protein surface include silyl orsubstituted silyl pendant groups, particularly alkoxysilyl pendantgroups. The addition polymerization typically is free radical-initiated,such as by thermal, photo, or redox free radical initiation. Thepolymerization may be carried out via bulk, emulsion or solutionpolymerization, although solution polymerization is the typical mediawhen carbon-unsaturated silane compounds are utilized.

The modified protein may be mixed with the carbon-unsaturated silanecompound to form a free radical polymerizable mixture. The free radicalpolymerizable mixture may include suitable radical initiators such asany thermal, redox or photo initiators. Illustrative initiators include,for example, alkyl peroxides, substituted alkyl peroxides, arylperoxides, substituted aryl peroxides, acyl peroxides, alkylhydroperoxides, substituted alkyl hydroperoxides, aryl hydroperoxides,substituted aryl hydroperoxides, heteroalkyl peroxides, substitutedheteroalkyl peroxides, heteroalkyl hydroperoxides, substitutedheteroalkyl hydroperoxides, heteroaryl peroxides, substituted heteroarylperoxides, heteroaryl hydroperoxides, substituted heteroarylhydroperoxides, alkyl peresters, substituted alkyl peresters, arylperesters, substituted aryl peresters, azo compounds and halidecompounds. Specific initiators include cumene hydroperoxide (CHP),t-butyl hydroperoxide (TBHP), t-butyl perbenzoate (TBPB), sodiumcarbonateperoxide, benzoyl peroxide (BPO), lauroyl peroxide (LPO),methylethylketone peroxide 45%, potassium persulfate, ammoniumpersulfate, 2,2-azobis(2,4-dimethyl-valeronitrile),1,1-azobis(cyclo-hexanecarbonitrile),2,2-azobis(N,N′-dimethyleneisobutyramidine) dihydrochloride,2,2-azobis(2-amidino-propane) dihydrochloride and2,2-azobis(2-amido-propane) dihydrochloride. Redox pairs such aspersulfate/sulfite and Fe(2+)/peroxide are also useful. The free radicalpolymerizable mixture may be subjected to suitable free radicalinitiation conditions such as heat, UV light irradiation, visible lightirradiation, electron beam irradiation, plasma, electrolysis and similarfree-radical generating schemes. The polymerization conditions(temperature, pH, pressure, etc.) may be readily determined to achievethe desired polymerization.

The molar ratio of the carbon-unsaturated silane compound (e.g.,monomer) to the modified polypeptide or protein may be selected tocontrol the desired degree of chain-extension polymerization. Morespecifically, the ratio of the moles of vinyl functionality in the vinylsilane compound to the moles of vinyl functionality in the modifiedprotein may be controlled. In other words, the proportion of vinylfunctional groups that are derivatized with a polymer chain and thelength of the polymer chain may be controlled, at least in part, by thesilane:protein molar ratio. The molar ratio of the carbon-unsaturatedsilane compound (e.g., monomer) to the modified polypeptide or proteinalso may be selected to control the desired degree of crosslinking ofthe alkoxysilyl functional groups as explained below in more detail. Ingeneral, the silane:protein molar ratio may range, for example, fromabout 20 to about 80,000, more particularly about 200 to about 20,000.

As mentioned above, the shell formation also involves a crosslinking ofthe silicon-containing functional group in addition to thechain-extension polymerization. The crosslinking may be accomplished,for example, by adding a separate crosslinking agent either during orafter the chain extension polymerization (e.g., the vinylpolymerization). However, in certain variants of the processes disclosedherein addition of a separate crosslinking agent is not required inorder to achieve the desired limited crosslinking for the individualpolymer shells. For example, the addition of a separate crosslinkingagent to promote crosslinking of the (meth)acryloxy-containingorganosilane compound typically is not necessary. Addition of a separatecrosslinking agent also may not be necessary in the case of the silanecompounds that do not contain (meth)acryloxy functional groups dependingupon the desired degree of crosslinking.

Instead of adding a separate crosslinking agent, the crosslinking caninvolve hydrolysis and condensation of the silicon-functional group. Forexample, the alkoxysilyl or hydroxysilyl functional groups can undergohydrolysis in an aqueous media. Additives such as water-soluble organicsolvents and salts may be added to the aqueous media to improve thehydrolysis. In general, the hydrolysis and condensation may be conductedat any temperature provided denaturation of the protein is avoided, buta range of about 4 to about 40° C. may be used as an example. The pH ofthe hydrolysis aqueous media may be controlled to be acidic, neutral orbasic, but a range of about 2 to about 11 may be used as an example.Typically, the pH of the hydrolysis/condensation is at or relativelynear the optimal pH of the protein for bioactivity. Buffer salts, acids,and/or bases may be used to control the pH. Examples of acids that maybe added include organic acids such as acetic acid and the like, and aninorganic acid such as hydrochloric acid, sulfuric acid, phosphoric acidand the like. Examples of an alkali that may be added include sodiumhydroxide, potassium hydroxide and the like. A catalyst or an additionalsilicon-containing compound (e.g., tetraethyl orthosilicate) may beadded to enhance the hydrolysis/condensation of the intermediateproduct.

The intermediate polymerization product that includes the alkoxysilaneor hydroxysilane functional groups may only be soluble in an organicsolvent. Thus, addition of an aqueous buffer solution to the organicphase-intermediate polymerization product results in a two-phase system.The modified protein particles undergo hydrolysis and condensation,causing movement of the hydrolyzed and condensed product from theorganic phase and into the aqueous phase. In other words, the hydrolyzedand condensed product is, in effect, extracted from the organic phaseinto the aqueous phase. The aqueous phase and the organic phase areseparated via any appropriate separation technique. The aqueous phasethen is filtered as described below in more detail to separateagglomerations and other particles larger than nanoparticle size,resulting in a filtrate that includes substantially only particles ofnanoparticle size. This extraction and filtration process may berepeated until no significant amount of protein activity is observed inan extraction filtrate. At this point, no additional extractions areperformed. Each one of the previously obtained extraction filtrates arethen mixed together to produce a final product. The final productcontaining the nanoparticles may be aged by placing the final product inan ambient temperature of about 4 to about 30° C. for an extended periodof time such as, for example, at least about 24 hours.

As mentioned above, acrylic acid or a (meth)acrylate is another monomerthat can be reacted with a vinyl-functionalized polypeptide or proteinmolecule. This addition polymerization could be performed in an aqueousbuffer. The vinyl-functionalized polypeptide or protein can be mixedwith water-soluble acrylic acid or (meth)acrylate in an aqueous buffer,and the vinyl polymerization can be initiated by UV radiation in thepresence of an initiator such as azobisisobutryonitrile. Thepolymerization product is a heterogeneous population that includes largepolymers or agglomerations as well as nanoparticles having an acrylicpolymer shell covalently bound to the polypeptide or protein molecule.The nanoparticles can be isolated via filtration from the heterogeneouspopulation of polymeric products.

Polyethylene is another modifier compound described above. In this case,the dialdehyde, isocyanate, or carbodiimide shell-forming compoundcauses crosslinking of the grafted polyethylene glycol-containing aminogroups. Polyethylene glycol (PEG) grafted with epoxy groups or maleicanhydride groups can be further crosslinked in the presence ofL-glycine. Another path is to employ a block copolymer ofPEG-alkoxysilane. The PEG domain of the block copolymer can be attachedto the protein molecule via a grafted epoxy or maleic anhydride group,and the alkoxysilane will be hydrolyzed and condensed to form a shellaround the protein molecule. The final product is a nanoparticle thatincludes the crosslinked polyethylene structure as a shell covalentlybound to the polypeptide or protein molecule.

As mentioned previously, there is another synthetic approach that wasreferred to as option (b) above. In this approach, the polypeptide orprotein modifier compound is itself a silane compound. A modifiercompound that includes an α, β-ethylenically unsaturated functionalgroup is not required. Instead, a functional group of the silanecompound is directly covalently bonded to the free amino, carboxyl,and/or sulfide groups at the surface of the polypeptide or proteinmolecule. Illustrative silane compounds that can serve as modifiercompounds are those that also include a group that is reactive with freeamino, carboxyl, and/or sulfide groups of the protein molecule. Suchamino and carboxyl-reactive groups are described above in connectionwith the modifier compound used in the option (a) synthesis approach.Specific examples in the case of silane compounds include succinylgroups (e.g., succinic anhydride-bearing silanes), an amino group, anepoxy group, or an isocyanato group. Bonding of the succinic anhydridegroup to the amino group of the polypeptide or protein molecule canoccur by contacting the succinic anhydride-bearing silane with thepolypeptide or protein molecule in an aqueous buffer solution. Bondingof the amino group of the silane compound with the amino group of thepolypeptide or protein molecule can occur via reaction of thepolypeptide or protein with the amino silane compound in the presence ofglutaraldehyde, toluene diisocyanate, or diphenylmethane diisocyanate inslightly basic aqueous conditions. The result is the formation of aglutaraldehyde or isocyanate linkage, respectively, between the aminogroups.

Polyethylene glycol compounds that have been modified to include atleast one silyl or substituted silyl group are additional examples ofsilane compounds that can be used in the option (b) synthesis procedure.As described above, polyethylene glycol compounds can be covalentlygrafted onto polypeptide or protein molecules.

The resulting bonded silane compound provides silyl or substituted silylfunctional groups on the surface of the polypeptide or protein molecule.The silyl or substituted silyl functional groups can then be crosslinkedvia hydrolysis and condensation as described above to form thepolysiloxane shell. One feature of the option (b) approach is thatwater-soluble silane compounds can be used. Illustrative water-solublesilane compounds include 3-(triethoxysilyl)propylsuccinic anhydride,aminopropyltriethoxysilane, aminopropyltrimethoxysilane,aminopropoysilanetriol, 3-aminopropyltris(methoxyethoxyethoxy)silane,N-(triethoxysilylpropyl)-O-polyethylene oxide urethane,N-(3-triethoxysilylpropyl)gluconamide,methacryloxypropyltris(methoxyethoxy)silane,isocyanatopropyltriethoxysilane, epoxypropoxytriethoxysilane,epoxyhexyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, andγ-glycidoxypropylmethyldiethoxysilane.

The resulting final synthesized product may be considered to be aprotein/polymer biocomposite. The desired nanoparticle-sizedbiocomposites may be isolated from the final synthesis product mixtureor solution, for example, via centrifuging, filtration, adsorption,absorption and similar separation or purification techniques. Accordingto certain examples, the final synthesis product includes solidprotein/polymer biocomposites dissolved, suspended or dispersed in aliquid media. The biocomposite-containing liquid is passed through atleast one filter having a maximum pore size of 1 μm, more particularly amaximum pore size of 0.2 μm, and more particularly a maximum pore sizeof 0.1 μm. Examples of such filters include membrane filters such assyringe filter units. Any membrane filters that can separate proteinsbased on their molecular weight can also be used, such as filters havinga respective molecular weight cut off (“MWCO”) of 3 kilodaltons, 10kilodaltons, 30 kilodaltons, 50 kilodaltons, and 100 kilodaltons. Anyprotein/polymer agglomerates and impurities having a dimension greaterthan the respective maximum pore size (e.g., greater than 1 μm), ofcourse, will be retained on the filter. Thus, only nanoparticle-sizedbiocomposites will be present in the filtrate. According to oneparticular example. the resulting filtrate can be washed on a filterhaving a desired MWCO in order to separate material that is too small tobe a protein nanocomposite. The concentration of biocompositenanoparticles may be adjusted, for example, by increasing or decreasingthe polypeptide or protein concentration during the initial synthesissteps or during the washing of the final synthesis product on a filtermembrane. It should be understood that filtration is not the onlytechnique available for isolating the biocomposite nanoparticles, andthat other separation techniques such as those mentioned above could beused.

It also should be recognized that any of the intermediate productsgenerated during any of the syntheses disclosed herein also may besubjected to separation techniques for isolating nanoparticle-sizedintermediate products. Such nanoparticle-sized intermediate productsthen can be employed for the subsequent synthesis steps. For example,mixing an aqueous glutaraldehyde solution with a protein moleculesolution in an aqueous buffer (pH about 7-10, temperature of about 4° C.to room temperature) may generate a wide range of crosslinked proteinparticles. The nanoparticle-sized particles may be separated with amembrane filter as described above. The generation of such nanoparticlesvia glutaraldehyde may be especially applicable for producing shellnanoparticles having containing than one protein molecule in the coreconstruct as described above. The glutaraldehyde-treated nanoparticlesmay then be subjected to further synthesis for forming the shell aroundthe nanoparticles.

The biocomposite nanoparticles can be provided in powder form, forexample, by introducing a large quantity of salts (e.g., KCl, NaCl,sodium phosphate, potassium phosphate, etc.) into the above-described,final nanoparticle-containing solution. The amount of added salt mayvary widely, but could range from about 40 to about 99 weight %. Theresulting mixture then can be subjected to lyophilization techniques toproduce the powder.

According to one variant on the use of the nanoparticles, the isolatedbiocomposite nanoparticles may be subjected to further crosslinking toform a matrix of crosslinked nanoparticles, wherein each ofnanoparticles retains its individual covalently-bound shell. Forexample, if the shell is a polyorganosiloxane, a mixture of thenanoparticles may be subjected to further silanol condensation or anadditional silane compound may be reacted with the nanoparticles toeffect crosslinking between the polymer shells of the nanoparticles.

An exemplification of the above-described synthesis is depictedschematically in FIG. 1 and chemically in FIG. 2. Vinyl modification isintroduced onto the surface of an enzyme molecule (designated “E” inFIG. 2) via reaction of acryloyl chloride with the free amino groups ofthe enzyme molecule. The vinyl-modified enzyme molecule is reacted witha silane monomer, methacryloxypropyltrimethoxysilane (“MAPS”). Theresulting intermediate product is an enzyme molecule that has beenderivatized to include polymer chains at the sites of the modified freeamino groups. The number n of repeating monomer units in the polymerchain may range, for example, from about 3 to about 100, moreparticularly from about 5 to about 20. The polymer chain in theintermediate product includes pendant trimethoxysilyl groups. Thesetrimethoxysilyl groups then undergo hydrolysis and condensation togenerate a single enzyme nanoparticle (“SEN”).

A feature of certain examples of the above-described syntheses is thatthe yield of biocomposite nanoparticles may range from about 35% toabout 95%, more particularly from about 50% to about 80%, based on thebioactivity of the protein in the biocomposite nanoparticle divided bythe initial bioactivity of the free or native protein prior to synthesisof the biocomposite nanoparticle. There are various options forincreasing the yield. For instance, in the variation that involves freeradical polymerization, the concentration of free radical initiator maybe reduced to increase the yield of nanoparticles. As an illustrativeexample, the free radical initiator concentration may range from about0.1 to about 10 weight %, based on the total amount of modified proteinand carbon-unsaturated silane compound. The amount of time in which theshell-forming polymerization is permitted to occur also can affect theyield. In general, the yield will increase with shorter reaction timesfor the shell-forming polymerization. A further factor increasing theyield is the iterative extraction performed during the hydrolysis andcondensation of the silyl or substituted silyl functional groups.

The activity and stability of the polypeptide or proteins in thebiocomposite nanoparticles may be readily determined, for example, byvarious enzymatic reactions with various substrates. In the example ofα-chymotrypsin, the proteolytic activity may be measured, for example,by a hydrolysis assay of N-succinyl -Ala-Ala-Pro-Phe p-nitroanilide(“TP”). Examples of biocomposite nanoparticles having a proteasemolecule core as disclosed herein may have a relative bioactivitystability of at least about 0.9 for at least about ten days, moreparticularly a relative bioactivity stability of at least about 1.0 forat least about four days. The relative bioactivity is measured as theratio of residual activity to initial activity (see FIG. 6 explained inmore detail below). The stability of the disclosed biocompositenanoparticles can extend the lifetime of enzymes in various applicationssuch as biosensors, bioremediation, detergents, enzymatic synthesis inthe pharmaceutical and food industries, and bio-hydrogen production fromrenewable bio-products.

The unique composition and structure of the nanoparticles describedherein can serve as the building blocks for further structures andmaterials. Reactions with the surface of the nanoparticles, either assynthesized or after further covalent modifications, can bond thenanoparticles to other molecules, macromolecules, particles, ormaterials. The biocomposite nanoparticles may be bonded to otherbiocomposite nanoparticles. The biocomposite nanoparticles may be bondedto nanoparticles of other materials such as metals, magnetic materials,metal oxides and plastics. The biocomposite nanoparticles may be bondedto micron-size particles of other materials such as metals, magneticmaterials, metal oxides, and plastics. The biocomposite nanoparticlesmay be bonded to other nanostructures such as nanotubes. Thebiocomposite nanoparticles may be bonded to macromolecules such as DNA,RNA, proteins, polysaccharides, or synthetic polymers. The combinationof biofunctional nanoparticles, such as single enzyme nanoparticles, toother structures and materials provides a means to createmultifunctional assemblies.

For example, a feature of a polyorganosiloxane shell is that it can bereadily modified to include other classes of chemical functionalities.The modification may be accomplished, for example, by using a vinylsilane monomer that also includes the desired additional functionality.The modifying vinyl silane monomer may be added during the vinylpolymerization or it may be added during the hydrolysis and condensationof the silicon-containing functional groups.

One desirable chemical functionality that can modify the shell is agroup that can impart solubility in a selected solvent. The solvent maybe a hydrophobic solvent or a hydrophilic solvent. A solubilizednanoparticle can offer the advantage of increased interaction betweenthe protein molecule in the core and a reaction media. As a furtherillustration, the shell could be modified to enhance its ability forattaching to surfaces, macromolecules, or biological substrates. Forexample, amino groups could be grafted onto the nanoparticle shell. Theamino-grafted nanoparticles then can be covalently bonded toamino-grafted deoxyribonucleic acid (DNA) via linkers such asglutaraldehyde. According to an additional variant, the shell of a firstnanoparticle and the shell of a second nanoparticle each could bemodified so that they can be covalently bonded with each other resultingin multifunctional nanoparticle assemblies. Following another approach,a mixture of different enzyme nanoparticles could be prepared and thenconsolidated such as, for example, by precipitation, by evaporating thesolvent, or by adding crosslinking agents to connect one nanoparticlewith another. Consequently, the multiple differing enzymes would be invery close proximity to each other, with their separation being definedby the thickness of two of the individual nanoparticle shells. Suchclose proximity will enhance the sequential conversion of a molecule bythe different enzymes compared to enzymes scattered in dilute liquids ormixtures of larger than nanoscale particles.

The thin and porous structure of the “armored” polymer shell allows foraqueous solubility of the biocomposite nanoparticles. This water-solublefeature can be used for homogeneously immobilizing biocompositenanoparticles on substrate surfaces, particularly nanostructuredmatrices such as nanoporous silica, carbon nanotubes, and conductivepolymers. The immobilization of the biocomposite nanoparticles will beextremely useful in various applications such as biosensing andbioconversion, since enzymes can be stabilized and the nanostructuredmatrices will provide a large surface area for the attachment of thebiocomposite nanoparticles. The immobilized biocomposite nanoparticlesmake it easy to purify the products after each bioconversion, and can beeasily recovered for the next-step bioconversion.

One specific example of a use for the enzyme nanoparticles involvesbioconversion of various substrates via enzymatic catalysis. Desirableapplications include degradation of toxic substances for bioremediation,and synthesis of various chemicals such as drug intermediates andpeptides. Conversion of the substrate to product may be controlled bytechniques such as those described in U.S. Pat. No. 5,719,039, whichalso describes various substrates suitable for enzymatic catalysis inassorted organic solvents.

Further specific uses of the enzyme nanoparticles include hydrolysisand/or transesterification of drug intermediates; enzymatic detergents;conversion of glucose to fructose (e.g., utilizing glucose isomerase);bioremediation employing laccase, tyrosinase, peroxidase,organophosphorous hydrolase, or dehalogenase for the decontamination oforganic contaminants such as phenols, pesticides, and halogenatedcompounds; biosensing using glucose oxidase, peroxidase, tyrosinasse, ororganophosphorous hydrolase; and hydrogen production using glucosedehydrogenase and hydrogenase.

An additional application involves the use of trypsin nanoparticles fortrypsin digestion in proteomic analysis. In the proteomic analysis ofproteins in a sample, trypsin is employed for digesting proteins intopeptides. The trypsin digestion takes a long time (usually an overnightincubation), and is difficult to automate due to the poor stability oftrypsin. The improved trypsin stability provided by the nanoparticleconstruct disclosed herein may prolong the lifetime of the trypsin, andthus reduce the incubation time.

Immobilization of the biocomposite nanoparticles on substrate surfacesalso offers a number of opportunities. For example, thepolyorganosiloxane shells may be readily adhered to silicate surfaces(e.g., glass, silicon wafer, and quartz) due to the presence of silylgroups in the polyorganosiloxane shells. In this case, the biocompositenanoparticles may be provided in a suitable carrier media such as anaqueous solution, and then the aqueous solution can be applied to thesubstrate surface. Drying of the aqueous solution will producebiocomposite nanoparticles immobilized on the substrate surface. Proteinchips often are constructed from silicate materials, and thus thebiocomposite nanoparticles could be adhered to the surface of a proteinchip. Adherence to other types of surfaces can be accomplished bygrafting desired functional groups into the silicon-containing polymershell molecular structure during the shell polymerization and formation.For example, the surface of the polymer shell could be functionalizedwith amino groups by including aminopropyltrimethoxysilane during thehydyrolysis/condensation of the silyl or substituted silyl groups.

EXAMPLES Example 1 Synthesis of Single Enzyme Nanoparticles that Containα-chymotrypsin (“SEN-CT”)

Modification and Solubilization of CT. The modification andsolubilization of CT were performed by adding 10 mg CT to 5 ml ofphosphate buffer (0.2 M sodium phosphate, pH 8.0). The enzyme solutionwas cooled to 0° C., and 4 μl of acryloyl chloride was gradually addedto the solution over 10 minutes in a stirring condition. Theacryloylated CT was recovered by gel filtration chromatography (SephadexG-25 gel, 100-300 μm).

Ten milliliters of an aqueous enzyme solution (containing 1 mg/mlacryloylated CT, 1% (viv) isopropanol, and 2 mM CaCl₂ dissolved in 10 mMBis-Tris buffer, pH 7.8) was contacted with an equal volume of hexanecontaining 2 mM AOT surfactant. The resulting two-phase mixture wasstirred vigorously at 22° C. for 5 minutes, and centrifuged at 7000 Gfor 10 minutes. Upon separation of the hexane phase from the aqueoussolution, the enzyme-surfactant complex was dried by evaporating hexanewith nitrogen-bubbling or under vacuum, and then reconstituted back intohexane when used for the further synthesis of SEN-CT. The concentrationof CT in the hexane phase was determined by UV absorption at 280 nmn.

Two-Step Polymerization. MAPS (297 μl) was added to 3 mg solubilized andacryloylated CT in 1.5 ml hexane. Vinyl group polymerization betweenMAPS and acryloylated CT was initiated by UV light (365 nm) in thepresence of the free radical initiator2,2′-Azobis-(2,4-dimethylvaleronitrile) (0.8 mg/ml). Polymerization wasperformed under UV illumination in a black box at room temperatureovernight, and some population of resulting polymers precipitated out inthe form of a white powder.

Subsequent hydrolysis and condensation of the trimethoxysilyl groups wasaccomplished by adding an equal volume of phosphate aqueous buffer (200mM phosphate buffer, pH 8.0) to the hexane phase of the vinyl grouppolymerization that contains the intermediate polymeric products. Theresulting two-phase system was vortexed and shaken at 22° C. and 300 rpmfor 5 minutes. The aqueous buffer phase was removed from the two-phasesystem by a syringe. The aqueous buffer phase was filtered by a syringefilter unit (with maximum pore size 0.1 μm), and produced a filtrateconsisting of a transparent solution that turned into a turbid solutionwithin 10-30 minutes. This extraction process was iterated (typically byabout four to five times) until no significant amount of CT activity wasobserved in the aqueous extraction filtrate in the latest iteration. Atthis point, no more extractions were performed. The individualextraction filtrates that were obtained in each iteration were thenmixed together to produce a final extracted aqueous buffer solution. Theextracted aqueous buffer solution contained the majority of the activeCT (at least about 85%), and was aged in the refrigerator at least for aday. The aged and turbid solution was filtered again by the syringefilter unit (with maximum pore size 0.1 μm), and further washedexcessively by buffer (10 mM phosphate buffer, pH 7.8) on a membranefilter (MWCO 10K: molecular weight cut-off 10,000). This washing processshould remove the autolytic products of CT and un-reacted agents such asMAPS and initiators. The final clear solution (having a fairlyhomogeneous population of SEN-CT) contains most of the initial activeCT, and was stored in a refrigerator (4° C.). The yield of active CT inthe form of SENs was 38-73% (calculated based on the total finalactivity of SEN-CT/the total initial activity of native CT beforesynthesis =0.38-0.73)

Example 2 TEM Imaging of the Biocomposite Nanoparticles

Transmission electron microscopy (“TEM”) images of the biocompositenanoparticles containing α-chymotrypsin (“CT”) synthesized as describedabove are shown in FIGS. 3, 4 and 5. The seemingly hollow center of thenanoparticle matches the size and shape of the CT, and results from thetransmittance of the electron beam through the protein structure. Thedark image surrounding the CT core is the polymer “armored” shell, andthe presence of silicon was confirmed by energy dispersive x-rayanalysis in the TEM instrument. It is apparent from the images of FIGS.3, 4 and 5 that the nanoparticles do not have a dimension greater thanabout 30-40 nm, and in some cases, 10-20 nm. FIG. 5 is of interest sinceit shows two protein molecules in the core of the nanoparticle.

The TEM images were obtained by further washing the final samples of theSEN-CT with distilled water on a membrane filter (MWCO 10K). The washedsamples were observed under a JEOL 2010 high-resolution analyticalelectron microscope (JEOL USA Inc., Peabody, Mass.). Variousconcentrations of SEN-CT were tested to obtain the images of thebiocomposite nanoparticles, which show the discrete nanoparticles, butalso contain a large number of nanoparticles. In other words, a rigorousoptimization of SEN-CT concentration was performed to prevent twoextremes: excessively high concentration resulting in the images of ablack layer having a lot of hollow spots; and insufficiently lowconcentration to capture a large number of SEN particles in an image.The presence of silicon in the armored shell of SEN-CT, which representsthe success of the SEN synthesis, was confirmed by the energy dispersiveX-ray analysis in the TEM instrument.

Example 3 Activity and Stability of the Biocomposite Nanoparticles

The CT activity was determined by the hydrolysis of N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide (“TP”) (1.6-160 μM) in an aqueous buffer(10 mM phosphate, pH 7.8) at room temperature (22° C.). The absorbanceincrease at 410 nm was monitored using a spectrophotometer (Model Cary5G UV-Vis-NIR spectrophotometer from Varian Inc., Palo Alto, Calif.),and converted to the initial hydrolytic rate at each substrateconcentration. Kinetic constants (k_(cat), K_(m), and k_(cat)/K_(m))were obtained by using software (Enzyme Kinetics Pro from ChemSW,Farifield, Calif.) that performs nonlinear regression based on the leastsquare method.

The active site concentration of both free CT and SEN-CT was determinedby the MUTMAC assay. In a typical procedure, 100 μl of free CT or SEN-CTsolution in various concentrations (10-1000 μg/ml) was mixed with 2 mlof 25 μg/ml MUTMAC solution (0.1 M sodium phosphate, pH 7.8). Thefluorescence emission at 450 nm (excitation at 360 nm) was measuredusing a PTI fluorescence system (Lawrenceville, N.J.) after the emissionintensity reached the plateau. A solution of 4-methylumbelliferone wasused as the standard. BCA assay (Pierce, Rockford, Ill.) was used todetermine the protein content in the CT sample. Tests with theout-of-bottle CT powder showed that 52.4 weight % was active by theactive site titration. On the other hand, SEN-CT resulted in 41.2 weight% active CT, and it suggests that 11.2 weight % of the initial active CTwas damaged during the SEN synthesis.

To assess the CT stability, residual activity was determined (in thesame way as mentioned earlier for the enzyme activity measurements)after incubation in aqueous buffer (10 mM phosphate, pH 7.8) at 30° C.for the pre-determined time intervals. In brief, a measured amount of CTsample was added to aqueous buffer in a centrifuge tube, and placed in atemperature-controlled incubator. After a predetermined incubation time,the tube was removed from the incubator and cooled to the roomtemperature. 10 μl of TP solution (10 mg/ml in DMF) was added directlyto the diluted aqueous enzyme solution in a cuvette, and the reactionrates were measured. For all tests, free CT was used directly from thebottle, and SEN-CT was used from the stock solution in aqueous buffer(10 mM phosphate, pH 7.8).

The stability of the CT biocomposite nanoparticle surprisingly did notshow any decrease in CT activity after four-day incubation in a buffersolution at 30° C., while free CT was inactivated very rapidly by anorder of magnitude (see FIG. 6). The CT biocomposite nanoparticlestarted to show about a 5-10% decrease of CT activity after ten-dayincubation. The inactivation of free CT was dependent upon the initialCT concentration, and showed a pseudo-first-order inactivation kinetic.Although not bound by any theory, it is believed that the stabilizationof the nanoparticle approach may be achieved via the prevention ofenzyme molecules from being denatured since the activity of SEN-CT iscomparable to free CT in both the hydrolysis of TP and the proteolysisof various proteins (described in more detail below). The crosslinkedand armored polymer shell plays a key role in this protection of enzymemolecules.

The storage stability of the CT biocomposite nanoparticles was alsoimpressive in a buffer solution. After a three-month storage of theSEN-CT in the buffer solution (10 mM phosphate buffer, pH 7.8) at 4° C.,82% of the SEN-CT activity remained in solution, and 18% of the CTactivity disappeared. However, it was noted that a transparent layer ofSEN-CT was built up on the inner surface of the vials. A potentiallysignificant portion of the absent 18% CT activity in the solution shouldhave been transported to the SEN-CT layer, which showed at least anappreciable amount of stable CT activity.

As described above, the activity of SEN-CT and free CT was measured bythe hydrolysis of N-Succinyl-Ala-Ala-Pro-Phe p-nitroanilide (TP) in abuffer solution (10 mM phosphate buffer, pH 7.8). The kinetic constants(k_(cat), K_(m), and k_(cat)/K_(m)) were obtained via nonlinearregression based on the least square method (Table 1). The catalyticefficiency (k_(cat)/K_(m)) of CT in the form of SENs was decreased byabout half, and it was due to reduced k_(cat). However, the bindingconstant (K_(m)) of SEN-CT was almost the same as that of free CT (i.e.,the OEF was 0.97). This suggests that the armored polymer shell did notcause any significant mass-transfer limitation for the substrate (TP).

TABLE 1 Kinetic constants of Free CT and SEN-CT in aqueous buffer.^(a)Sample k_(cat)(s⁻¹)^(b) K_(m)(μM) k_(cat)/K_(m) (× 10⁵ M⁻¹s⁻¹)^(b) FreeCT 29.9 ± 0.7 38.9 ± 2.7 7.70 ± 0.06 SEN-CT 13.8 ± 0.6 40.2 ± 4.6 3.44 ±0.04 SEN-CT/Free CT 0.46 1.03 0.45 ^(a)The CT activity was determined bythe hydrolysis of TP (1.6-160 μM) in an aqueous buffer (10 mM phosphate,pH 7.8) at room temperature (22° C.). The absorbance increase at 410 nmwas monitored using a spectrophotometer, and converted to the initialhydrolytic rate at each substrate concentration. Kinetic constants(k_(cat), K_(m), and k_(cat)/K_(m)) were obtained by using software(Enzyme Kinetics Pro) that performs nonlinear regression based on theleast square method. ^(b)The active site concentration was determined bythe MUTMAC assay. In a typical procedure, 100 μl of free CT or SEN-CTsolution in various concentrations (10-1000 μg/ml) was mixed with 2 mlof 25 μg/ml MUTMAC solution (0.1 M sodium phosphate, pH 7.5). Thefluorescence emission at 450 nm (excitation at 360 nm) was measuredafter the emission intensity reached the plateau. A solution of4-methylumbelliferone was used as the standard.

Example 4 Effective Porosity of Biocomposite Nanoparticles

The effective porosity of the CT biocomposite nanoparticles wasinvestigated by the proteolytic activity of CT against various proteins(insulin, apomyoglobin, aldolase, and albumin). The proteolytic activitywas measured by the OPA assay, in which OPA reacts with primary amines,formed by the proteolytic cleavage of peptide bonds, and fluoresces(λ_(ex)=347 nm; λ_(em)=445 nm). In brief, 100 μl of 1 mg/ml targetprotein was mixed with 10 μl of 0.1 mg/ml free CT or 0.2 mg/ml SEN-CT[to maintain the similar proteolytic activity] in aqueous buffer (10 mMphosphate buffer, pH 7.8), and incubated at 40° C. After apre-determined incubation time, the aliquot (10 μl) from each sample wasdiluted (1/100) in 1 ml borate buffer (200 mM sodium borate buffer, pH9.5), and the proteolysis was stopped by adding 100 μl of PMSF solution(2 mg/ml in isopropanol). 0.75 ml of diluted sample was mixed with 1.5ml OPA reagent solution (Sigma P0532, complete reagent containing bothOPA and 2-mercaptoethanol). The fluorescence emission at 445 nm(excitation at 347 nm) was measured after the OPA reaction was allowedto proceed at room temperature (22° C.) for 2 minutes. The initial rateof proteolysis (Em445/h) was obtained from the increase of fluorescenceemission within 1-3 hours, and converted to the initial rate ofamino-group formation (μM/h) based on the result of OPA assay withL-tyrosine standard.

To assess the effective porosity of SEN-CT, we incubated variousproteins together with SEN-CT. Since CT is a protease, the proteolyticproducts can be detected when the substrate proteins can pass throughthe armored polymer shell of SEN-CT. All substrate proteins werecarefully selected, and are of the highest purity (standard proteins forthe purpose of calibrating and testing mass spectrometers). Noimpurities should be in the substrate proteins since the proteolysis ofimpurities can mask off the proteolysis of target proteins. Thedetection of proteolytic products was performed by the OPA(orthophthaldialdehyde) method, measuring the amount of amino groups,which are formed by the proteolytic activity of CT. The increase ofemission at 445 nm (excitation at 347 nm) was measured time-dependently,and converted to the initial rate of amino-group formation. The initialrates are compared to those with free CT (see Table 2). There was nocritical difference between free CT and SEN-CT in their proteolyticactivity against various proteins even though there are some variations.This suggests that the effective porosity of SEN-CT is large enough forSEN-CT to be active against large protein such as bovine serum albumin(molecular weight 66 kilodaltons).

TABLE 2 Proteolysis of various proteins by free CT and SEN-CT.^(a)Initial Rate Initial with Rate with Free CT SEN-CT Protein Source MWμM^(b) (μM/h) (μM/h) Insulin Bovine 5734.51 159 31 20 ApomyoglobinEquine 16952.27 54 4 13 Aldolase Rabbit Muscle 39212.28 23 30 19 AlbuminBovine Serum 66430.09 14 43 49 ^(a)The proteolysis was measured by theOPA assay. Each substrate protein (100 μl of 1 mg/ml) was mixed with 10μl of 0.1 mg/ml free CT or 0.2 mg/ml SEN-CT to maintain the similarinitial activity, and incubated at 40° C. After a pre-determinedincubation time, the aliquot (10 μl) from each sample was diluted into 1ml borate buffer (200 mM sodium borate buffer, pH 9.5), and theproteolysis was stopped by adding 100 μl of PMSF solution (2 mg/ml inisopropanol). The portion of diluted sample (0.75 ml) was mixed with 1.5ml OPA reagent solution, and the fluorescence emission at 445 nm(excitation at 347 nm) was measured after the OPA reaction for 2minutes. The initial rates of proteolysis were calculated from thetime-dependent emission increase, based on the OPA assay with theL-tyrosine standard. ^(b)Initial concentration of each substrate protein[0.91 mg/ml] in the incubation solution with CT.

Example 5 Polyethylene Glycol (PEG)/Protein Nanoparticles

Epoxy functional groups can be grafted onto PEG (nonfunctionalized,MW_(n) ca 200-10,000) via reaction with epichlorohydrin in an aqueousbuffer (pH of about 2-12) or an organic solvent such as methanol. Theresulting epoxy-PEG can be contacted with protein molecules in anaqueous buffer (pH of about 7-10). The amino groups on the surface ofthe protein molecules will react with the epoxy group of the epoxy-PEG,and form protein-linear PEG composites. The protein-linear PEGcomposites in the aqueous buffer may subsequently be excessively washedon a first membrane filter having a maximum pore size of 0.1 μm and thenon a second filter having a lower MWCO of 10K. The filtered product thencan be mixed with a polyethyleneimine (PEI) solution in buffer (pH about2-12), and shaken at about 50 to about 250 rpm for a time period rangingfrom about 10 minutes to about 2 hours until the PEI can be entangledwith the PEG structure around the protein molecules. After excessivemixing, glutaraldehyde treatment (1-5% glutaraldehyde for about 10minutes or 2 hours) may be performed to crosslink the PEI structurearound the protein molecules in an aqueous buffer (pH about 7-10) at thetemperature range of 4° C. to room temperature. The final proteinnanoparticles encapsulated in the crosslinked PEI-PEG can be furtherwashed on two membrane filters with excessive aqueous buffer (pH optimalfor enzyme activity, pH 2-12).

Example 6 Polyethylene Glycol (PEG)/Protein Nanoparticles

Commercially available PEG, functionalized with epoxy or maleicanhydride, can be contacted with protein molecules in an aqueous bufferwith a molar excess of PEG over protein (molar ratio ranging from about10 to about 1000). There will be crosslinking between the amino groupsof the protein molecules and epoxy (or maleic anhydride) of PEG, and thecrosslinked products in an aqueous buffer can be washed on a firstmembrane filter having a maximum pore size of 0.1 μm and then on asecond membrane filter having a lower MWCO of 10K. This washingprocedure will result in the separation of protein-PEG nanoparticles.After excessive washing, a diamine (such as L-lysine or PEI) can beadded to induce further crosslinking around the individual proteinmolecules. This final product can be washed again on two membranefilters (a maximum pore size of 0.1 μm and a lower MWCO of 10K).

Example 7 Siloxane/Protein Nanoparticles

Epoxy-polydimethylsiloxane (PDMS) solubilized in hexane, and proteinmolecules dissolved in an aqueous buffer solution (pH of about 7-10) maybe mixed together. The resulting two-phase system can be shaken topromote a reaction between the epoxy-PDMS and the amino groups of theprotein molecules, and extraction of the protein-PDMS product into thehexane phase. The hexane phase containing well-solubilized and hydratedprotein-PDMS may be collected, and tetraethyl orthosilicate (TEOS) canbe added for silicate formation around the protein molecules. PDMSpolymers of various molecular weights can be selected as a spacer forpreventing the agglomeration of protein-silicate nanoparticles.

Instead of using epoxy-PDMS, PDMS-PEG can be used for the solubilizationof protein in hexane, and TEOS can be added into the separated hexanephase containing hydrated protein-PEG-PDMS. The added TEOS will behydrolyzed and condensed around each individual protein molecule, andwill result in an “armored” shell protecting the individual proteinmolecules. In this example, there may be no covalent bonds between theprotein molecules and the PEG.

1. A composition comprising a plurality of discrete particles, eachparticle comprising at least one polypeptide molecule and at least onepolymer covalently bound to the polypeptide molecule so as to form acrosslinked polymer shell substantially encompassing the polypeptidemolecule, wherein substantially all of the particles each individuallydo not define a dimension greater than about 1 μm, the polymer isselected from the group consisting of a silicon-containing polymer, apolyethylene glycol polymer, an acrylic polymer or a mixture orcombination thereof, and each crosslinked polymer shell is notcrosslinked with the other crosslinked polymer shells.
 2. Thecomposition according to claim 1, wherein the polymer comprises asilicon-containing polymer.
 3. The composition according to claim 1,wherein the polypeptide comprises an enzyme.
 4. The compositionaccording to claim 3, wherein the enzyme comprises chymotrypsin,trypsin, subtilisin, papain, a lipase, horseradish peroxidase, soybeanperoxidase, chloro peroxidase, manganese peroxidase, tyrosinase,laccase, cellulase, xylanase, lactase, sucrase, organophosphohydrolase,cholinesterase, glucose oxidase, alcohol dehydrogenase, glucosedehydrogenase, hydrogenase, glucose isomerase or a mixture thereof. 5.The composition according to claim 1, wherein the composition comprisesa liquid composition that includes the particles.
 6. The compositionaccording to claim 1, wherein the polymer shell is sufficiently porousso that the polypeptide molecule can digest a substrate having amolecular weight up to about 70 kilodaltons.
 7. The compositionaccording to claim 6, wherein the polymer shell has an average thicknessof about 0.2 to about 200 nm.
 8. The composition according to claim 1,wherein substantially all of the particles each individually do notdefine a dimension greater than about 50 nm.
 9. The compositionaccording to claim 1, wherein substantially all of the particles containa single protein molecule.
 10. The composition according to claim 1,wherein substantially all of the particles contain at least two enzymemolecules that can perform a sequential reaction on a substratemolecule.
 11. The composition according to claim 1, wherein there is afirst particle comprising a first polypeptide molecule, and at least oneadditional particle comprising at least one second polypeptide moleculethat is different than the first polypeptide molecule.
 12. Thecomposition according to claim 11, wherein the distance between thefirst polypeptide molecule and the second polypeptide molecule isdefined by the combined thickness of the shell encompassing the firstparticle and the shell encompassing the additional particle.
 13. Acomposition comprising a plurality of particles, each particlecomprising at least one enzyme molecule and at least onesilicon-containing polymer covalently bound to the enzyme molecule so asto form a silicon-containing polymer shell substantially encompassingthe enzyme molecule, wherein substantially all of the particles eachindividually do not define a dimension greater than about 1 μm.
 14. Thecomposition according to claim 13, wherein the enzyme compriseschymotrypsin, trypsin, subtilisin, papain, a lipase, horseradishperoxidase, soybean peroxidase, chloro peroxidase, manganese peroxidase,tyrosinase, laccase, cellulase, xylanase, lactase, sucrase,organophosphohydrolase, cholinesterase, glucose oxidase, alcoholdehydrogenase, glucose dehydrogenase, hydrogenase, glucose isomerase ora mixture thereof.
 15. The composition according to claim 13, whereinthe silicon-containing polymer comprises a polyorganosiloxane.
 16. Thecomposition according to 13, wherein the particles are discreteparticles, and each silicon-containing polymer shell is not crosslinkedwith each other.
 17. The composition according to claim 13, wherein thesilicon-containing polymer shell has an average thickness of about 0.2to about 200 nm.
 18. A particle comprising at least one protein moleculeencompassed within a crosslinked polymer shell that is bound to theprotein molecule, wherein the particle does not define a dimensiongreater than about 100 nm, and exhibits an observed effectiveness factorof at least about 0.7.
 19. The particle according to claim 18, whereinthe polymer shell comprises a silicon-containing polymer, a polyethyleneglycol polymer, an acrylic polymer or a mixture or combination thereof.20. The particle according to claim 19, wherein the protein comprises anenzyme and the silicon-containing polymer shell comprises apolyorganosiloxane.
 21. The particle according to claim 19, wherein theparticle does not define a dimension greater than about 50 nm.
 22. Theparticle according to claim 19, wherein the polymer shell issufficiently porous so that the protein can digest a substrate having amolecular weight of at least about 70 kilodaltons.
 23. The particleaccording to claim 19, wherein the silicon-containing polymer shell hasan average thickness of about 0.2 to about 50 nm.
 24. The particleaccording to claim 19, wherein the particle contains a single proteinmolecule.
 25. The particle according to claim 19, wherein the particlecontains at least two enzyme molecules that can perform a sequentialreaction with a substrate molecule.
 26. A substrate defining at leastone surface, wherein the particles of claim 1 are immobilized on thesubstrate surface.
 27. The substrate according to claim 26, wherein thesubstrate comprises a silicate material selected from glass, siliconwafer, fused silica, or quartz.
 28. The substrate according to claim 26,wherein the substrate comprises nanoporous silica, a silicon nanowire, acarbon nanotube, a carbon nanorod, or a conductive polymer.
 29. A methodfor enzymatically hydrolyzing a substrate, comprising contacting thesubstrate with the particles of claim
 1. 30. A method for enzymaticallyhydrolyzing a substrate, comprising contacting the substrate with theparticle of claim
 18. 31. The method of claim 29, wherein thepolypeptide molecule of the composition of claim 1 comprises trypsin,and the substrate comprises a protein.
 32. The method of claim 30,wherein the protein molecule of the particle of claim 17 comprisestrypsin, and the substrate comprises a second protein.
 33. Thecomposition according to claim 1, wherein the polymer comprises apolyethylene glycol polymer.
 34. The composition according to claim 1,wherein the polymer comprises an acrylic polymer.
 35. A compositioncomprising a plurality of particles, each particle comprising at leastone polypeptide molecule and at least one polymer covalently bound tothe polypeptide molecule so as to form a crosslinked polymer shellsubstantially encompassing the polypeptide molecule, whereinsubstantially all of the particles each individually do not define adimension greater than about 100 nm and the polymer selected from thegroup consisting of a silicon-containing polymer, a polyethylene glycolpolymer, an acrylic polymer or a mixture or combination thereof.
 36. Thecomposition according to claim 35, wherein the polymer is asilicon-containing polymer.
 37. The composition according to claim 35,wherein the polypeptide comprises an enzyme.
 38. The compositionaccording to claim 37, wherein the enzyme comprises chymotrypsin,trypsin, subtilisin, papain, a lipase, horseradish peroxidase, soybeanperoxidase, chloro peroxidase, manganese peroxidase, tyrosinase,laccase, cellulase, xylanase, lactase, sucrase, organophosphohydrolase,cholinesterase, glucose oxidase, alcohol dehydrogenase, glucosedehydrogenase, hydrogenase, glucose isomerase or a mixture thereof. 39.The composition according to claim 35, wherein the composition comprisesa liquid composition that includes the particles.
 40. The compositionaccording to claim 35, wherein the polymer shell is sufficiently porousso that the polypeptide molecule can digest a substrate having amolecular weight up to about 70 kilodaltons.
 41. The compositionaccording to claim 40, wherein the polymer shell has an averagethickness of about 0.2 to about 50 nm.
 42. The composition according toclaim 35, wherein substantially all of the particles each individuallydo not define a dimension greater than about 50 nm.
 43. The compositionaccording to claim 35, wherein substantially all of the particlescontain a single protein molecule.
 44. The composition according toclaim 35, wherein substantially all of the particles contain at leasttwo enzyme molecules that can perform a sequential reaction on asubstrate molecule.
 45. The composition according to claim 35, whereinthere is a first particle comprising a first polypeptide molecule, andat least one additional particle comprising at least one secondpolypeptide molecule that is different than the first polypeptidemolecule.
 46. The composition according to claim 45, wherein thedistance between the first polypeptide molecule and the secondpolypeptide molecule is defined by the combined thickness of the shellencompassing the first particle and the shell encompassing theadditional particle.
 47. The composition according to claim 35, whereinthe polymer is a polyethylene glycol polymer.
 48. The compositionaccording to claim 35, wherein the polymer is an acrylic polymer. 49.The composition according to claim 35, wherein each crosslinked polymershell is not crosslinked with the other crosslinked polymer shells.